Centrifuging liquid-solids mixtures



March 9, 1965 c. M. AMBLER 3,172,851

CENTRIFUGING LIQUID-SOLIDS MIXTURES Filed Aug. 31, 1962 "mg 0 2 -55 INVENTOR.

3 CHARLES M.AMBLER W 3M 2DNv.Lsans A80 ATTQR NEY United States Patent G 3,172,851 CENTREFUGING LlQUlD-SOLlDS MIXTURES Charles M. Ambler, Philadelphia, Pa, assignor to Pennsalt Chemicals Corporation, a corporation of Pennsylvania Filed Aug. 31, 1962, Ser. No. 229,835 5 Claims. (Cl. 2337) This invention relates to separating solids from liquidsolid mixtures. More specifically, this invention relates to the separation from a liquid-solids mixture of solids of relatively small particle size and having little difference in density from the liquid of the mixture.

In the prior art the separation of some types of solids, e.g. crystalline solids, from liquid-solids mixtures has been accomplished in a zone of centrifugal force. In one type of such processing the mixture has been introduced to the zone and the solids, being of greater density than the liquid, have settled about the periphery. The settled solids have been engaged by a conveying surface and moved inward of the liquid-vaponinterface to discharge separately from the liquid. An apparatus by which such processing may be accomplished is disclosed in the U8. Patent 2,679,974, issued June 1, 1954, to F. P. Gooch. The apparatus may comprise a hollow rotor with axial feed means, the rotor having an opening at either end, the second opening being spaced inward from the first. Disposed axially within the rotor is a screw conveyor rotating at a speed different from the speed of the rotor. In operation the solids settle against the wall of the rotor and the conveyor engages the settled solids and plows them up a beach to discharge them through the second opening. The liquid-vapor interface in such an apparatus has been set by the position of the first opening through which liquid discharges and invariably the inter face has been well outward from the second opening. The solids, therefore, in their travel up the beach inward of the liquid-vapor interface drain before discharging through the second opening with reduced moisture content.

The process and apparatus referred to above has been entirely satisfactory for separating liquid from certain types of solids which are characterized by a combination of density, consistency, and size which has enabled them to be conveyed or scrolled up the beach as by the conveyor described above. The process and apparatus has been limited in its application, however, in that solids in many liquid-solids mixtures simply defy such a scrolling operation. As the cause of this uncooperative characteristic, it has been assumed that such solids do not pack to scrollable consistency so that when they do reach the beach section they simply flow back into the liquid. It has further been assumed that the greatest problem occurs at the liquid-vapor interface where the effective density changes from the difference between their true density and the mass of liquid they displace to their actual true density with no change in consistency. For these solids such a process has been inapplicable and an alternative has been taken to, for instance, the solid bowl centrifuge having peripheral nozzles through which such nonscrollable solids may be discharged. It has been found, however, that such an alternative has produced solids of undesirably high liquid content.

There has consequently been an unsatisfied need for a process and apparatus for separating solids not susceptible to the classic approach with the conveyor-type centrifuge described above. My present invention satisfies this need and is predicated on my discovery that what would have been regarded as non-scrollable solids may be separated from a liquid-solids mixture by employing a centrifuge of the conveyor type, modified in a manner which produces unexpected results.

Further features and advantages of the invention, and the manner in which they have been obtained will be evident from a reading of the following illustrative detailed description and reference to the drawings in which:

FIGURE 1 is an elevational view partly in section and partly schematic, of an apparatus embodying the invention; and

FIGURE 2 is a graph indicating the predictability of the apparatus and process of the invention in accomplishing a concentration.

Briefly, my invention involves the process of separating solids from a liquid-solids mixture, the solids being of relatively small particle size and having little difference in density from the liquid, including the steps of feeding the mixture to a zone of centrifugation at a feed point, settling the solids, discharging the separated liquid at a first position, engaging the settled solids with a conveying surface and moving the solids with the surface axially away from the first position and the feed point and toward a second position radially outward from the first position to form automatically a dam of settled solids adjacent the second position, the dam extending inward of the first position to block substantially the flow of liquid to the second position, and discharging the separated solids outward from the second position. The invention further involves apparatus by which the process of the invention may be accomplished.

Referring more specifically to the drawings, an apparatus embodying my invention is generally designated 1t As shown, the apparatus comprises a frame 12 including a pair of spaced aligned bearing units 14. A rotor 16 comprises a peripheral wall and a pair of spaced end walls with shaft extensions mounted to rotate within the bearing units 14. A constant speed motor may be connected to the rotor driving pulley 22. Rotatably mounted within the rotor as shown is a conveyor element 24 having helical flights 26 and a feed opening 28 intermediate its ends. A conveyor drive shaft 30 which extends axially within an opening of shaft 18, is adapted to drive the conveyor at a speed diiferent from that of rotor 16, receiving its power from rotor 16 through a gearbox 32 of structure similar to that disclosed in the above-identified Gooch patent. Pulley 34 may also be driven by a motor of variable speed to control the speed differential between the conveyor 24 and rotor 16, in a manner also well known in the art. Feed is delivered to opening 28 through feed tube 36.

The leftward end Wall of the rotor as shown in FIG- URE 1 is formed with a large opening 38 spaced inwardly from the outermost inside surface of the peripheral wall of the rotor. The opening 38 is preferably covered by a conventional adjustable plate with a smaller opening 49 in registry with opening 38 and providing liquid discharge to a radial level a, the level of the liquid interface. In the peripheral wall of the rotor adjacent its rightward end is a radially outward directed opening 42 comprising the solids discharge opening, the edge of this opening over which solids may discharge is at a level b outward from the level a of opening 40. Approaching the opening 42 is a filler section having for instance a frusto-conical inner surface comprising beach 44 up which the solids may be moved toward the opening 42 by the flights 2.6. The outer edges of the flights are cut to terminate adjacent the beach in this area.

A cover 46 is partitioned to collect separately the discharged solids and liquid as is conventional.

With the apparatus in operation in accordance with the process of my invention, the feed comprising a liquidsolids mixture is continuously introduced through feed tube 36 and feed opening 28 into the rotor 16 at a feed point. The solids are permitted to settle against the wall of the rotor (FIGURE 1). The separated liquid is dis charged through opening 40 to define the liquid-vapor interface at level a. The rotor 16 and conveyor 24 are rotated in the same direction but at slightly different speeds to effect a rightward movement by the flights 26 of the solids toward the solids discharge port 42. As the solids with which the invention is particularly applicc ble are moved rightwardly, they presumably form in a short time a dam D immediately to the left of opening 42 blocking the passage of liquid out through this opening. Continued movement of the solids causes a portion of the solids comprising the dam to continuously discharge through the port with reduced moisture content. Other solids continuously move up to replace those discharged and to comprise the darn.

The discovery was made and the invention perfected in the concentration of brewers yeast. While the following discussion uses yeast as an illustration of solids for which the invention is applicable, the invention is not so limited in its application.

In a yeast recovery stage from a beer brewing process a liquid-solids mixture comprising dilute beer and yeast was fed to a nozzle centrifuge. Typical of such a machine is the Nozljector centrifuge available from The Sharples Corporation of Philadelphia, Pennsylvania. From the nozzles of this centrifuge the solids discharged in a yeast slurry which analyzed at 9.62% solid matter, the remainder water and solubles. This slurry was fed in the first example below to the conventional apparatus of the general type described in the afore entioned patent of F. P. Gooch. In the second example the slurry was fed to an apparatus embodying the invention.

Example I The nozzle discharge was delivered to an apparatus of the type described by Gooch and designated P-3000 by its manufacturers, The Sharples Corporation. The rotor had an inside length of approximately 30%" and an inside diameter of about 14". It was driven at 4000 rpm. and the conveyor was rotated in the same direction at a differential of 15 r.p.m. The solids discharge port was positioned inward of the liquid discharge port to provide a beach up which solids could be scrolled to drain before discharge. The radial dilferential between the two ports was set at A Feed was delivered to the rotor at 150 pounds per hour dry basis. The operation was not stable on extended runs in that after a quarter of an hour or so at a constant rate the liquid efiluent that had been clear started to surge and was alternately clear and full of yeast.

Example 2 The apparatus was modified from Example 1 in accordance with the invention, all other conditions remaining the same. The level of the liquid discharge port was moved inward to become inward of the solids discharge port. With this differential it was observed that on start-up all of the feed liquid at the beginning discharged from the solids discharge end as would be expected. After some two or three minutes liquid flow at this end stopped and liquid began to discharge from the liquid discharge port and two or three minutes subsequent yeast discharged continuously from the solids discharge port with good stability of operation over several hours. This discharge analyzed at 19.0% solids. The feed rate was increased and clear eifluent was obtained at rates of dry solids basis yeast discharge of over 400 pounds per hour at 16.6% dry substance content. FIG- URE 2 indicates the predictable relationship between pounds dry substance and the percent dry substance of the discharge.

It was found that by increasing the rotational speed to 4700 rpm. at the same port settings for any given flow rate, moisture content of the solids discharge is reduced by about 1%.

As has been indicated, it is suspected that the satisfactory results obtained in the practice of the invention are attributable to the natural tendency of the solids in being scrolled to form a dam blocking the passage of the liquid to the solids discharge port. The force of the liquid behind the solids of the dam assists discharge.

It is highly preferably in practicing the process of the invention that the solids discharge port be outward of the liquid discharge port, for if the solids discharge port is equal to or inward of the liquid discharge port the inability to scroll of the solids with which the invention is applicable results in surging of the discharges and instability. Further, by having the solids discharge out- Ward the force of the inward liquid makes discharge of the solids that much easier.

It should be reiterated that the invention is not only applicable to the separation of yeast solids from diluted beer, this being merely an example, the invention has other applicability, for instance, in the concentration of corn gluten and in other slurries, the solids of which have heretofore been regarded as non-scrollable. I have thus developed an apparatus and process which may be used successfully in the concentration of solids which are not normally susceptible to processing in a worm-type centrifuge. The apparatus and process involve a simple modification to a presently available machine to produce results which are totally new and wholly unexpected. These results are characterized by clean liquid discharge, continuous stable operation, and better concentration of solids than heretofore available from the centrifugal processing of these certain mixtures.

It is to be understood that the above particular description is by way of illustration, and that changes, omissions, additions, substitutions, and/ or modifications may be made therein without differing from the apparatus of the invention. Therefore, it is intended that the patent shall cover the various features of patentable novelty that reside in the invention.

1 claim:

1. A process for separating solids from a liquid-solids mixture, the solids being of relatively small particle size and having little difference in density from said liquid, including the steps of (a) feeding the mixture to a zone of centrifugation at a feed point, the zone having a liquid discharge opening adjacent one end and a solids discharge opening at the other end and outward of said liquid discharge opening but inward from the outermost periphery of the zone,

(b) settling the solids, I

(c) discharging the separated liquid through said liquid discharge opening,

(d) engaging the settled solids with a helical surface coaxial with the zone and moving the solids with the helical surface axially away from the liquid discharge opening inward to said solids discharge opening, the solids discharge opening being of more than ample dimension to pass without restriction material which is available to it,

(e) discharging the separated solids through said solids discharge opening,

whereby the settled solids form a dam extending inward of the solids discharge opening, the dam being relatively impervious to the liquid and substantially blocking its escape through the solids discharge opening.

2. A process as described in claim 1 wherein the solids comprise yeast solids and the liquid comprises diluted beer.

3. A process as described in claim 1 wherein the helical surface extends about the axis for at least 360.

4. A centrifuge for separating solids from a liquidsolids mixture, the solids being of relatively small particle size and having little diiferencc in density from said liquid, the centrifuge comprising (a) a hollow bowl mounted to rotate about an axis and having a portion of its inner surface decreasing in diameter approaching one end and having a solids discharge opening at the said end and a liquid discharge opening at the opposite end, the solids discharge opening being outward from the liquid discharge opening,

(b) a helical conveyor disposed within the bowl and on said axis and extending substantially the inside length of the bowl and having flights with distal edges generally complementing the contour of the inside of the bowl, the conveyor being adapted in turning relative to the bowl to move settled solids inward over said portion to said solids discharge opening, the solids discharge opening being of more than ample dimension to pass without restriction material which is available to it,

(c) a feed tube extending along the axis to deliver feed liquid into the bowl,

(d) means to drive the bowl and the conveyor at different speeds whereby the solids in being moved by the conveyor toward the solids discharge opening form a darn extending inward of the solids discharge opening, the dam being relatively impervious to the liquid and substantially blocking its escape through the solids discharge opening.

5. A centrifuge as described in claim 4 wherein the helical conveyor extends about the axis for at least 360.

References Cited by the Examiner UNITED STATES PATENTS 535,306 3/95 Stewart 2337 X 2,612,314 9/52 Huelsdonk 233-7 2,625,320 1/53 Lyons 2337 2,679,974 6/54 Gooch 2337 2,711,854 6/55 Kjellgren 2337 2,733,856 2/56 Kjellgren 2337 2,743,865 5/56 Graae 2337 2,766,930 10/56 Schmiedel 2337 2,795,635 6/57 McBride.

2,862,658 12/58 Dahlgren 2337 3,096,282 7/63 Trotter 233--7 FOREIGN PATENTS 372,679 6/ 32 Great Britain.

HARRY B. THORNTON, Primary Examiner.

ROBERT F. BURNETT, Examiner. 25 

4. A CENTRIFUGE FOR SEPARATING SOLIDS FROM A LIQUIDSOLIDS MIXTURE, THE SOLIDS OF RELATIVELY SMALL PARTICLE SIZE AND HAVING LITTLE DIFFERENCE IN DENSITY FROM SAID LIQUID, THE CENTRIFUGE COMPRISING (A) A HOLLOW BOWL MOUNTED TO ROTATE ABOUT AN AXIS AND HAVING A PORTION OF ITS INNER SURFACE DECREASING IN DIAMETER APPROACHING ONE END AND HAVING A SOLIDS DISCHARGE OPENING AT THE SAID END AND A LIQUID DISCHARGE OPENING AT THE OPPOSITE END, THE SOLIDS DISCHARGE OPENING BEING OUTWARD FROM THE LIQUID DISCHARGE OPENING, (B) A HELICAL CONVEYOR DISPOSED WITHIN THE BOWL AND ON SAID AXIS AND EXTENDING SUBSTANTIALLY THE INSIDE LENGTH OF THE BOW AND HAVING FLIGHTS WITH DISTAL EDGES GENERALLY COMPLEMENTARY THE CONTOUR OF THE INSIDE OF THE BOWL, THE CONVEYOR BEING ADAPTED IN TURNING RELATIVE TO THE BOWL TO MOVE SETTLED SOLIDS INWARD OVER SAID PORTION TO SAID SOLIDS DISCHARGE OPENING, THE SOLIDS DISCHARGE OPENING BEING OF MORE THAN AMPLE DIMENSION TO PASS WITHOUT RESTRICTION MATERIAL WHICH IS AVAILABLE TO IT, (C) A FEED TUBE EXTENDING ALONG THE AXIS TO DELIVER FEED LIQUID INTO THE BOWL, (D) MEANS TO DRIVE THE BOWL AND THE CONVEYOR AT DIFFERENT SPEEDS WHEREBY THE SOLIDS IN BEING MOVED BY THE CONVEYOR TOWARD THE SOLIDS DISCHARGING OPENING FORM A DAM EXTENDING INWARD OF THE SOLIDS DISCHARGE OPENING, THE DAM BEING RELATIVELY IMPERVIOUS TO THE LIQUID AND SUBSTANTIALLY BLOCKING ITS ESCAPE THROUGH THE SOLIDS DISCHARGE OPENING. 